Landing gear assembly

This invention relates to a landing gear assembly, and in particular to a steerable landing gear assembly intended for use in the nose landing gear of an aircraft.

The nose landing gear assembly of an aircraft typically comprises a hydraulic or pneumatic shock absorber arranged to carry, at its lower end, a wheel support housing carrying one, or preferably a pair of wheels arranged coaxially with one another on opposite sides of the wheel support housing. Where it is desirable to be able to adjust the orientation of the wheels to assist in steering of the aircraft whilst on the ground, at least part of the shock absorber may be angularly adjustable, adjustment of the angle thereof adjusting the orientation of the wheel support housing, and hence the axes of the wheels. Such adjustment may be achieved using, for example, a rack and pinion arrangement powered hydraulically or electrically through associated torque links.

Such landing gear assemblies have the advantage that the steering mechanism is located away from the wheel assembly and so is subject to relatively low shock loadings, in use, but the disadvantage that the shock absorber and torque linkage has to be designed in such a manner as to permit the transmission of the steering loads to the wheels.

According to the present invention there is provided a landing gear assembly comprising a wheel support housing rotatably connected to a support member, the wheel support housing containing an electrically powered motor operable to adjust the angular position of the wheel support housing relative to the support member.

It will be appreciated that by using an electrically powered motor located in the wheel support housing to control the angular position of the wheel support housing, the shock absorber or other support device, of which the support member forms part, does not need to be able to rotate or to transmit rotary or angular movement to the wheel support housing and no torque link assembly is required. Consequently, it can be of much simplified form. Further, compared to arrangements in which steering control is achieved hydraulically, control is much easier to achieve.

The electrically powered motor may be of the radial flux type, or could be an axial flux, pancake motor. The use of an electric pancake motor may be advantageous in that further space saving may be possible.

Conveniently, the wheel support housing further houses a gear train mechanism, for example in the form of an epicyclic gear arrangement, connected to the output of the electrically powered motor.

Preferably, a clutch arrangement is provided, disengagement of the clutch arrangement permitting angular movement of the wheel support housing relative to the support member independently of the operation of the electrically powered motor.

One or more sensors may be provided to allow monitoring of the angular position of the wheel support housing relative to the support shaft. The sensor may comprise, for example, a Hall effect sensor, a shaft position encoder or an RVDT.

The support member preferably comprises a lower piston tube or shaft of a shock absorber, the lower piston tube being keyed to an upper piston tube or shaft of the shock absorber. Conveniently, the upper and lower piston tubes are keyed to one another by a ball spline coupling, which enhances the stiffness of the assembly.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

<figref idrefs="DRAWINGS">FIG. 1</figref> is a view illustrating part of a landing gear assembly in accordance with one embodiment of the invention; and

<figref idrefs="DRAWINGS">FIG. 2</figref> is a view, to a larger scale, and in greater detail, illustrating part of the assembly of <figref idrefs="DRAWINGS">FIG. 1</figref>.

Referring to the accompanying drawings there is illustrated part of a landing gear assembly comprising a multi-part wheel support housing <b>10</b> rotatably mounted to the lower end of a shock absorber <b>12</b>. The shock absorber <b>12</b> is connected to the remainder of an aircraft's nose landing gear (not shown) and comprises an upper, outer piston tube <b>14</b> and a lower, inner piston tube <b>16</b>, the inner and outer piston tubes <b>14</b>, <b>16</b> being dimensioned to allow telescoping movement therebetween. A piston member <b>18</b> is located within the inner piston tube <b>16</b> and forms a seal therewith in the usual manner. A ball spline coupling <b>20</b> is provided between the upper and lower piston tubes <b>14</b>, <b>16</b> the coupling <b>20</b> accommodating relative axial movement therebetween but preventing or substantially preventing relative angular movement therebetween such that the lower piston tube <b>16</b> is non-rotatably mounted to the remainder of the landing gear, thereby enhancing the stiffness of the assembly.

The wheel support housing <b>10</b> incorporates a pair of axle regions <b>22</b> arranged coaxially with one another and adapted to support associated wheels <b>24</b> for rotation relative to the wheel support housing <b>10</b>.

As best shown in <figref idrefs="DRAWINGS">FIG. 2</figref>, the wheel support housing <b>10</b> is rotatably mounted to the lower piston tube <b>16</b> by a series of bearings <b>26</b>, thus the lower piston tube <b>16</b> forms a support member for the wheel support housing <b>10</b>. The bearings <b>26</b> accommodate rotary or angular movement of the wheel support housing <b>10</b> relative to the lower piston tube <b>16</b>, but prevent or restrict relative axial movement therebetween.

Located within the wheel support housing <b>10</b> is an electrically powered motor <b>28</b>. In the arrangement illustrated, the motor <b>28</b> is a radial flux motor of relatively short axial length, but it will be appreciated that other forms of electrically powered motor may be used. For example, it may be preferred to use an axial flux motor, and the use of a pancake motor may be preferred as this may allow additional space savings to be made. The motor <b>28</b> comprises a stator <b>30</b> which is fixed relative to the wheel support housing <b>10</b>, and a rotor <b>32</b> which is rotatable relative to the wheel support housing <b>10</b> when the motor <b>28</b> is operating. The rotor <b>32</b> is coupled to an output gear <b>34</b> which encircles but is free to rotate relative to an adjacent part of the lower piston tube <b>16</b>.

The output gear <b>34</b> is arranged to serve as an input, in use, to an epicyclic gear train <b>36</b>. The gear train <b>36</b> includes a sun gear <b>38</b> upon which a series of idler gears <b>40</b> are mounted. The sun gear <b>38</b> encircles, but is free to rotate relative to, the lower piston tube <b>16</b>. The idler gears <b>40</b> are each in meshing engagement with the output gear <b>34</b> and also with teeth formations (not shown) provided on the adjacent part of the wheel support housing <b>10</b>. It will be appreciated that, in use, upon operation of the motor <b>28</b>, the output gear <b>34</b> rotates and this drives each idler gear <b>40</b> for rotation about its respective axis of rotation. The meshing of the idler gears <b>40</b> with the teeth formations provided on the wheel support housing <b>10</b> causes the idler gears <b>40</b> to precess around the lower piston tube <b>16</b>, hence driving the sun gear <b>38</b> for rotation. The precise number of idler gears <b>40</b> provided is not important and it is envisaged that around six such gears will be provided. The provision of this arrangement results in the sun gear <b>38</b> rotating, in use, at a speed lower than the output gear <b>34</b>.

The gear train <b>36</b> further includes a plurality of planetary gears <b>42</b>, each of which includes a first toothed region <b>44</b> which meshes with both the sun gear <b>38</b> and with tooth formations (not shown) provided on the adjacent part of the wheel support housing <b>10</b>, and a second toothed region <b>46</b> which meshes with teeth provided on an output ring gear <b>48</b>. In operation, the output ring gear <b>48</b> is held against rotation relative to the lower piston tube <b>16</b> by a clutch arrangement <b>53</b> as will be described below. The first and second toothed regions <b>44</b>, <b>46</b> of the planetary gears <b>42</b> have a slightly different number of teeth to one another, for example the number of teeth may differ by only one or two. It will be appreciated that rotation of the sun gear <b>38</b> results in the planetary gears <b>42</b> each rotating about its respective axis of rotation, and the meshing between the planetary gears <b>42</b> and the wheel support housing <b>10</b> causes the planetary gears <b>42</b> to precess around the lower piston tube <b>16</b>. The precessing motion of the planetary gears <b>42</b>, in combination with the small difference in the number of teeth between the first and second regions <b>44</b>, <b>46</b> of the planetary gears <b>42</b> results in the wheel support housing <b>10</b> being driven for rotation or angular movement relative to the fixed, or earthed, output ring gear <b>48</b>. The speed at which the wheel support housing <b>10</b> is driven relative to the fixed output ring gear <b>48</b> is much lower than the rotary speed of the rotor <b>32</b> and output gear <b>34</b>.

An annular support member <b>50</b> engages the planetary gears <b>42</b>, supporting the gears <b>42</b> for movement as described hereinbefore.

The output ring gear <b>48</b> is shaped to define a cylindrical upstand <b>52</b> within which a clutch arrangement <b>53</b> is provided. The clutch arrangement <b>53</b> comprises a first series of clutch plates <b>54</b> which are keyed or splined to the upstand <b>52</b> so as to be rotatable or angularly movable therewith but to be capable of limited axial movement. Interposed between the clutch plates <b>54</b> are a second series of clutch plates <b>56</b> which are splined or keyed to the lower piston tube <b>16</b> so as to be rotatable or angularly moveable therewith and capable of limited axial movement relative thereto. A shoulder member <b>58</b> is secured to the lower piston tube <b>16</b>, and an armature <b>60</b> is biased by means of springs <b>62</b> towards the shoulder member <b>58</b>. The clutch plates <b>54</b>, <b>56</b> are located between the armature <b>60</b> and the shoulder member <b>58</b>, thus the biasing of the armature <b>60</b> urges the clutch plates <b>54</b>, <b>56</b> into engagement with one another, thereby restricting relative angular movement therebetween, and hence between the lower piston tube <b>16</b> and the output ring gear <b>48</b>.

An actuator including a toroidal coil <b>64</b> is arranged to move the armature <b>60</b> against the action of the springs <b>62</b>, when energised, to permit relative angular movement to occur between the clutch plates <b>54</b>, <b>56</b>, and hence allow relative movement between the lower piston tube <b>16</b> and the output ring gear <b>48</b>.

In normal use, the coil <b>64</b> is deenergised, and so the springs <b>62</b> serve to urge the armature <b>60</b> to a position in which the clutch plates <b>54</b>, <b>56</b> are compressed, thus the clutch is engaged and the output ring gear <b>48</b> is secured against significant angular movement relative to the lower piston tube <b>16</b>. In this condition, operation of the motor <b>28</b> under the control of an electronic motor controller <b>29</b>, and gear train <b>36</b>, to drive the output ring gear <b>48</b> for rotation relative to the wheel support housing <b>10</b> will cause the wheel support housing <b>10</b> to move, angularly, relative to the lower piston tube <b>16</b>, and hence relative to the remainder of the landing gear, thereby changing the orientation of the axes of the wheels <b>24</b> and achieving steering. When the motor <b>28</b> is not operating, the nature of the gear train <b>36</b> is such that a very large external load would need to be applied to the wheel support housing <b>10</b> to achieve angular movement thereof, and so the wheel support housing <b>10</b> is effectively braked against such movement.

Should it be desired to allow the angular position of the wheel support housing <b>10</b> to be adjusted by the application of an external loading, then the coil <b>64</b> is energised resulting in movement of the armature <b>60</b> against the action of the springs <b>62</b>, reducing the compression of the clutch plates <b>54</b>, <b>56</b> and effectively disengaging the clutch <b>53</b>. The disengagement of the clutch <b>53</b> allows the output ring gear <b>48</b>, and hence, via the gear train <b>36</b>, the wheel support housing <b>10</b>, to undergo angular movement relative to the lower piston tube <b>16</b> under the action of such an externally applied loading.

Although the clutch <b>53</b> described hereinbefore is of the type which is engaged when the coil is deenergised, energisation of the coil disengaging the clutch, arrangements which operate in the opposite manner, ie are engaged when energised and disengaged when deenergised, are also envisaged. Such an arrangement may be preferred in order to provide a deenergised default condition in which the wheel support housing <b>10</b> may be readily moved by external forces.

In order to assist in controlling the operation and steering of the landing gear assembly, it may be desirable to provide one or more sensors <b>66</b> operable to monitor the angular position of the wheel support housing <b>10</b> relative to the lower piston tube <b>16</b>. The sensors <b>66</b> could take a range of forms. For example, they could comprise Hall effect type sensors, shaft position encoders or RVDTs. The output of the sensors <b>66</b> may be used by the motor controller <b>29</b> in controlling the operation of the motor <b>28</b>.

As the entire shock absorber <b>12</b> is non-rotating, in use, steering being achieved by using the motor <b>28</b> and gear train <b>36</b> integrally located within the wheel support housing <b>10</b> to drive the wheel support housing <b>10</b> for angular movement relative to the lower piston tube <b>16</b> of the shock absorber <b>12</b>, it will be appreciated that the provision of torque links to transfer steering torques through the shock absorber and to the wheel support housing can be avoided. Further, the location of the motor <b>28</b> permits access thereto for maintenance and servicing operations to be performed in a relatively simple and convenient manner. The use of an electrically powered motor to achieve steering simplifies the associated control system, compared to hydraulically driven arrangements.

It will be appreciated that a number of modifications and alterations may be made to the arrangement described hereinbefore without departing from the scope of the invention.